One type of earth boring drill bit, particularly for oil and gas wells, has three rotating cones angling inward toward the center axis of the drill bit. The cones are mounted on bearing pins of legs that extend downward from a bit body. Each cone has a backface closely spaced to a portion of the bit leg called a last machined surface. As the body rotates about its axis, each of the cones simultaneously rotates about its own axis. Drilling mud is pumped down the drill string and flows out of nozzles on the drill bit body. The mud and cuttings return up an annulus surrounding the drill string.
It has long been recognized in the drill bit industry that the longevity of rotary cone drill bits is increased if foreign material or debris such as mud is prevented from entering the bearings associated with each of the cones. Drill bits used in carrying out rotary drilling have been subject to wear and damage by virtue of erosion caused by the abrasive effect of the foreign materials present in the drilling process. Mud and solids from the earthen formation pack onto certain portions of the bit structure, including the gage surface. Mud packing on the gage surface can cause mud and cuttings to pack into the seal gland, hindering performance. The rate of penetration can be limited by excessive contact with the borehole wall. Drilled solids adhering to a cone's surface will increase the amount of contact with the borehole wall, and may reduce penetration rates.
In the past, various versions have been employed to address the foregoing problem. Devices to mechanically deflect foreign material from between the cone backface and the leg are known, such as pins mounted to the bit leg in close proximity to the backface. These devices are somewhat helpful in solving the problem of material build-up in some respects, but fail to contribute to the removal of mud cuttings in other respects.